312 A SHORT HISTORY OF SCIENCE 



devised a simple method of counting the number of vibrations 

 corresponding with each note. 



THE BEGINNINGS OF MODERN IDEAS OF HEAT: LATENT AND 

 SPECIFIC HEAT ; CALORIMETRY. The earlier ideas of the nature 

 of heat are not unlike those of light. Theories of emission were 

 at first preferred for both, and present ideas of vibration or 

 undulation have appeared only recently. Heat was even re- 

 garded as an imponderable yet material substance, " caloric," 

 emitted by hot bodies and absorbed by cold ones. High temper- 

 ature meant the presence, and low temperature, the absence, of 

 caloric. The rise of mercury in the thermometer tube was ex- 

 plained as due to the expansion of the mercury not, as to-day, by 

 increase of distance between molecules, but by the addition of 

 caloric and the consequent increase of total material. Francis 

 Bacon remarked on the problem of heat and in an interesting 

 passage on the proper method of its study shows that he knew 

 many of its phenomena, including its development "in bodies 

 heated by rubbing." But it remained for Black, of Edinburgh, 

 whose work on fixed air or carbonic acid we have dwelt upon 

 above, to make the fundamental researches which paved the 

 way both for the study of the theory of heat by Rumford at the 

 end of the eighteenth century, and for its industrial uses by 

 Watt in steam engineering in the middle of that century. Black, 

 while experimenting on heating and cooling, discovered that 

 heat may be applied to boiling water, or to water containing 

 melting ice, without raising the temperature. Obviously, such 

 applied heat must either be lost or somehow become latent. 

 Further experiments showed that once the ice is all melted, or 

 once the escape of steam is stopped by covering the water in a 

 closed vessel, the temperature begins to rise ; the heat is no longer 

 concealed, lost, or absorbed, but produces obvious effects. Ap- 

 parently the lost heat was somehow used in melting the ice and 

 in making the steam. These and other experiments by Black 

 proved suggestive to Watt, who at this time was trying to improve 

 upon the air-and-steam engine of Newcomen, in which atmos- 

 pheric pressure was used to push a piston in a cylinder filled with 



